The present invention relates to a method for detecting removal of organic material from a semiconductor device in a manufacturing process. At least one semiconductor device with deposited organic material is inserted into a fluid for removing the organic material from the semiconductor device.
In the technical field of manufacturing of semiconductor devices, the semiconductor devices usually are formed like disks or wafers for producing e.g. semiconductor chips. In the process of manufacturing of e.g. a semiconductor wafer, it is common and necessary to apply various process steps to the wafer. Especially lithographic processes are applied frequently in the process. Before applying a lithographic process, the wafer usually is deposited with at least one material layer such as organic photoresist material. Structures over the front side of the wafer can be performed. The structured photoresist layer then usually serves as a mask for further etching processes.
After a final etching process, it usually becomes necessary to remove the remaining portions of the photoresist layer before a next process or process step is applied. For removing organic material such as photoresist material from a semiconductor wafer it is common to use fluid acids with ingredients such as sulphuric acid and hydrogen peroxide. To this end, the fluid acid is enclosed in a reactor or a fluid bath container in which at least one semiconductor wafer with a deposited layer of photoresist material is to be inserted. In the removing process, the organic material carbon components of the photoresist material are oxidized and form reaction products such as carbon dioxide, the hydrogen components are formed into water. The fluid acid (so-called piranha bath) usually is heated up to e.g. 130xc2x0 C.
In such a process one often has to deal with the problem that photoresist residues are left on the wafer after the process ends. Also, some implanted kinds of resist are difficult to strip. Good tuning of the process is necessary. Under microscope it is very difficult to detect residuals of photoresist. Wafers having photoresist residues left on the wafer surface usually do not fulfill the strong requirements of modern semiconductor manufacturing. Photoresist residues can have a negative influence with respect to the process or process steps.
It is accordingly an object of the invention to provide a method for detecting the removal of organic material from a semiconductor device in a manufacturing process that overcomes the above-mentioned disadvantages of the prior art methods of this general type, which is suitable for detecting an incomplete removal of organic material, i.e. photoresist deposited on a processed semiconductor device.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for detecting the removal of organic material from semiconductor devices in a manufacturing process. The method includes inserting at least one semiconductor device having deposits of the organic material into a fluid for removing the organic material from the semiconductor device, producing measurement data for measuring a concentration of at least one reaction product formed by a reaction of the organic material and the fluid, and processing the measurement data to get a data curve. The semiconductor device is removed from the fluid. At least one of a turning point in the data curve, a local maximum point in the data curve and a local minimum point in the data curve are queried. The turning point of the data curve, the local maximum point of the data curve and the local minimum point of the data curve are each significantly different from signal noise after removing the semiconductor device from the fluid. A decision is made as to whether further processing of the semiconductor device is needed in dependence on the query results.
The method is applicable to various semiconductor devices with deposited organic material such as wafers for the manufacturing of semiconductor chips. For example, the semiconductor device contains a deposited layer of photoresist material. Moreover, various types of fluids can be used which are suitable for removing the organic material from the semiconductor device. Especially, a fluid is used having ingredients for removing the photoresist material. Preferably, sulphuric acid and at least one of hydrogen peroxide or ozone are inserted as fluid ingredients for removing photoresist material.
According to the invention, a clear identification even of small process problems that can lead to resist residues on a semiconductor device is made possible. The semiconductor device with deposited organic material is inserted into the fluid for removing the organic material from the semiconductor device. Then, measurement data are produced when measuring a concentration of at least one reaction product formed by the reaction of the organic material and the fluid. The measurement data are then processed to get a data curve.
In the case of resist residues left on the wafer, a concentrated dark piranha/resist mixture drops back into the fluid of the bath from the wafer during wafer removal at the process ends. This results in a clear turning point of the curve, a local maximum point of the curve and a local minimum point of the curve each being significantly different from signal noise, since the concentration of the measured reaction product changes quite rapidly. So, according to the invention, with querying for at least one of such a turning point, a local maximum point or a local minimum point of the curve after the process ends an incomplete removal of organic material, i.e. photoresist deposited on the processed semiconductor device can be detected. To this end, only easy mathematical calculations are necessary. This information then can serve as a basis for deciding on further processing of the semiconductor device dependent on the query result.
Preferably, the concentration of the at least one reaction product is measured with an optical sensor system. To this end, the system measures the transparency of the process fluid. The optical sensor system emits optical radiation and receives emitted optical radiation. Thereby, the optical radiation is emitted towards the fluid. With the receiving of the optical radiation that is transmitted through the fluid the transparency of the process fluid can be detected. The process fluid is not clear if it contains unoxidized portions of the removed organic material. The method can be fully automated. The signal produced by the optical sensor system is independent on normal pollution effects since the signals influenced by such effects are usually not in the course of the data curve. Therefore, the effects can easily be filtered.
The insertion of at least one of the ingredients such as hydrogen peroxide can be controlled due to the sensor signal. The controlling of the insertion can be performed in a manner that the consumption of the hydrogen peroxide in relation to the process time is optimized.
If the received optical radiation intensity is filtered with respect to minima signal peaks an influence of bubbles induced by the process can be overcome. The bubble-induced minima peaks of the sensor signal resulting from scattered light are then filtered.
In accordance with an added mode of the invention, there is the step of inserting the semiconductor device into the fluid for continued processing if one of the turning point of the data curve, the local maximum point of the data curve or the local minimum point of the data curve is detected.
In accordance with an additional mode of the invention, there is the step of marking the semiconductor device as a faulty device and sorting out the semiconductor device from the manufacturing process if one of the turning point of the data curve, the local maximum point of the data curve or the local minimum point of the data curve is detected.
In accordance with another mode of the invention, there is the step of querying for at least two turning points of the data curve after the semiconductor device is removed from the fluid.
In accordance with a further mode of the invention, there is the step of smoothing the data curve when processing the measurement data.
In accordance with a concomitant mode of the invention, there is the step of inserting the semiconductor device having at least one layer of photoresist material into the fluid.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for detecting removal of organic material from a semiconductor device in a manufacturing process, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.